The invention relates to an electric lamp provided with:
A glass lamp vessel having an axis and seals in mutual opposition on said axis; PA1 an electric element arranged in the lamp vessel; PA1 current conductors connected to the electric element and each embedded in a respective seal and comprising an external metal wire which issues to the exterior from said seal.
Such an electric lamp and a luminaire for this lamp are known from U.S. Pat. No. 4,929,863.
The known lamp has a lamp cap at either end around the respective seal with an electrical contact which is connected to the relevant external metal wire. A conductor in a luminaire may be fixed onto the electrical contact, for example by means of a flat eye or hook cable tag present at the conductor, and clamped tightly onto the contact by means of a nut. The lamp consumes a comparatively high power of 1600 to 2000 W. This power implies that comparatively strong currents are passed through the contacts, which in their turn may assume comparatively high temperatures which involve the risk of corrosion.
The known lamp is mechanically held in the luminaire at the lamp caps by lampholders and is electrically supplied through the contacts of the lamp caps.
An alternative luminaire with lampholders for, for example, the known lamp mentioned above is known from EP-A-0,643,258.
U.S. Pat. No. EP 95 201 891.1 (U.S. Pat. No. 5,729,080) describes an electric lamp in which there are no lamp caps around the seals at the ends. A bare metal wire issues to the exterior from each seal, while a mounting member, on which a luminaire can grip the lamp mechanically, is present at a distance from each end on each seal.
U.S. Pat. No. 5,412,275 discloses a lamp whose lamp vessel is fixed at one point in a lamp cap, while a molybdenum wire issues to the exterior-from a second end of the lamp vessel, having a welded joint of good quality with a wire of nickel/manganese 98/2. The latter wire extends to inside the lamp cap, surrounded by an insulating sleeve for the major part, and is fastened to a contact member of this lamp cap.
High temperatures in a contact spot may cause corrosion of the mutually contacting conductors, which will lead to high contact resistances and thus to electrical losses, indeed to extinguishing of the lamp. Major temperature fluctuations owing to high operating temperatures may also give rise to a loosening of a clamped connection formed by a nut tightened onto a contact member. This increases the temperature as well as the risk of corrosion. It is known that, for example, molybdenum often used as a metal for the external metal wire corrodes at room temperature already.